The present invention relates generally to detecting and responding to brown out events in a semiconductor chip. More particularly, the present invention relates to a brown out detector circuit for resetting semiconductor chips during brown outs.
A brown out is a common condition in an electrical system of low supply voltage (VDD) that impacts correct system operation. Brown outs may be caused by a variety of ordinary glitches, including inadequate power regulation, powering up or down system components, and software bugs. Portable electronic devices, such as cellular phones and cameras are particularly susceptible to brown outs, because the tenuous connection between the device's battery and its terminal may be jarred by even slight movements.
During a brown out, if the VDD drops below the required voltage of the electrical system, data may be corrupted and the chip may malfunction. Because the condition of circuit elements is lost during the brown out, the chip must then be reset to resume operation. Therefore, accurate brown out detection and subsequent chip reset is vital to ensuring reliable operation in most electrical systems.
In general, a voltage level or brown out detection circuit, which is coupled to the chip, is used to prevent data corruption and chip malfunction. The detection circuit typically is used not only to detect when VDD falls below a minimum operating voltage, but also when it rises back to a stable operating voltage. When VDD falls below the minimum detection threshold voltage, the detection circuit generates a chip reset signal to set logic within the chip to a known state. Therefore, when VDD returns to a stable operating potential, the chip may resume operation from the reset state.
Because of the strong demand for portability, it has become increasingly important for electronic devices to minimize power use to conserve battery life. Unfortunately, typical voltage level detectors require a steady state current to operate, which in turn drains the battery. In addition, the low operating voltage levels of portable devices leave much less margin of error for the detectors to operate within.
Other power saving features of portable devices, such as sleep and hibernation modes, also present problems. Because the VDD changes dramatically when a portable device enters sleep mode and may resemble a brown out, the voltage detector must be able to differentiate between the two events. For example, if a system reset is triggered when the device hibernates, the chip may malfunction.
Accordingly, it would be desirable to have a brown out detector that consumes very little power and operates reliably in low voltage systems having power saving features.